Currently, numerous methods exist for applying a coating or thin film of material to a sheet or strip of material. One conventional method of coating a continuous strip of sheet material is to submerse the sheet material in a bath of the coating material. This can be accomplished by pulling the sheet material through the bath of coating material, and then wiping off any excess coating material. This method has many drawbacks. One drawback to this method is the difficulty to control the amount of coating material applied to each side of the sheet material. Another drawback is the inability to apply different coating materials to each side of the sheet material. Also, this method often wastes a certain amount of the coating material during the wiping step.
Another method of applying a coating or thin film of material to a sheet or strip of material is to employ a spray coater or atomizer. In such a method, the coating material is electrostatically disposed on the sheet material. A spray coater in accordance with this method is disclosed in U.S. Pat. No. 4,839,202.
Still other types of coating methods include passing the sheet material through various applicators which deposit a thin film onto the sheet material with or without electrostatic assistance. The applicators can be either stationary members or rotatable members. One example of such a coating apparatus, which uses a pair of oppositely disposed applicators, is disclosed in U.S. Pat. No. 5,549,752 to Hahn et al. The Hahn patent discloses passing a continuous strip of material between a pair of oppositely disposed applicators for applying a thin film thereto. In one embodiment, two stationary wicks directly contact the sides of the continuous strip of material to apply a coating to both sides of the sheet material. In another embodiment, the wicks apply the coating material to two feed rolls which contact the sides of the sheet material to apply a thin film of coating material thereto. One drawback to this type of coating apparatus is that it lacks the ability to adjust the amount of coating material being supplied to various sections of the applicators.
Other examples of prior coating apparatuses are disclosed in U.S. Pat. No. 4,601,918 to Zaman et al.; U.S. Pat. No. 4,604,300 to Keys et al.; U.S. Pat. No. 4,712,507 to Helling; and U.S. Pat. No. 4,995,934 to Janatka.
In view of the above, it will be apparent to those skilled in the art that there exists a need for an improved coating apparatus which utilizes a plurality of metering devices to control the flow of coating material to the applicators for obtaining the desired coating on a pair of opposed sides of a substrate or sheet material. This invention addresses this need in the art, along with other needs which will become apparent to those skilled in the art once given this disclosure.